The disclosed technology relates to a lubricant composition with selected detergents suitable for providing reduced deposits when lubricating a marine diesel engine cylinder.
Lubrication of marine diesel engines, and in particular their cylinders, is challenging in part because of the types of fuel consumed by such engines, which may lead to an increased susceptibility to deposit formation compared with other internal combustion engines. Marine diesel cylinder lubricants are used for one pass and are consumed, rather than being retained in a sump. Such lubricants typically require a high detergent level, imparting high levels of basicity as measured by Total Base Number (TBN) to the lubricant, typically resulting in TBN levels of 25 or greater, such as 30 or greater, such as 40 or greater, 50 or greater, or 70 or greater, and typically up to 100 or to 100 or to 80. Often, phenate detergents of various types have been employed, and they have been more or less successful in controlling deposit formation.
However, there has recently been raised concern that phenate detergents may contain certain amounts of objectionable substituted phenols such as paradodecylphenol (PDDP) as byproducts or unreacted starting materials. PDDP has come under attention recently as a possible reprotoxicant, that is, a material that may cause harm to unborn children. Accordingly, there is a desire to reduce the amount of PDDP in lubricant additives, and that is presumed to involve reducing the amount of phenate detergent employed. Reducing the amount of phenate detergent, however, will have detrimental effects on the amount of deposit formation in a marine diesel engine and, absent some solution, would be unacceptable.
Various chemical means are potentially available for reducing deposit formation, but each has its real or perceived drawbacks. Sodium detergents, such as sodium sulfonate detergents, have been examined for their deposit reducing characteristics, but the use of sodium compounds in marine diesel lubricants typically leads to other problems. In particular, fuels for marine diesel engines typically contain a certain amount of vanadium (not normally present in distillate fuels for gasoline or diesel engines), which, in combination with alkali metals such as sodium can, under some circumstances, lead to the formation of metal vanadates which can be responsible for a problem which is known in the industry as “hot corrosion.” In a different combustion environment, U.S. Patent Application 2004/0118032, Aradi et al., Jun. 24, 2004, discloses manganese compounds to inhibit both low and high-temperature corrosion in utility and industrial furnace systems. There is discussion in paragraphs 0003, 0004, and 0051 of this document of the mechanisms by which sodium vanadate may form and promote corrosion. The fuel disclosed in Aradi may also contain a catalyst package that may be composed of one or more of Li, Na, K, Mg, Ca, Sr, Ba, Mo, Fe, Co, Pt, or Ce.
U.S. Patent Application Publication 2005/0209110, Roski et al., Sep. 22, 2005, discloses lubricating compositions containing at least 3 weight percent of (a) an overbased sulphonate detergent and at least 1.5 weight percent of (b) a sulphur containing phenate detergent. The composition is suitable for internal combustion engines, particular marine diesel applications to provide improved cleanliness, decreased cylinder wear and reduced deposits. Metals usable in the detergents include an alkali metal such as lithium, sodium or potassium; or an alkaline earth metal such as magnesium, calcium, or barium. There is also disclosure that for detergents in general (in addition to those described as components (a) and (b)), most commonly used metals include sodium, magnesium, calcium or mixtures thereof.
U.S. Pat. No. 5,804,537, Boffa et al., Sep. 8, 1998, discloses a crankcase lubricant, especially a low phosphorus passenger car motor oil, with a tri-metal detergent mixture. The lubricant is characterized by unexpectedly superior engine deposit performance. The tri-metal detergent mixture may comprise at least one calcium overbased metal detergent, at least one magnesium overbased metal detergent and at least one sodium overbased metal detergent. The total TBN contributed to the oil composition by said tri-metal detergent mixture is from about 2 to about 12.
The disclosed technology, therefore, solves the problem of maintaining good deposit control and low corrosion in a marine diesel lubricant, while reducing the amount of phenolic detergent present, by the careful selection and balancing of detergent components.